Capsules containing roast and ground coffee in which hot water flows under gravimetric force through the capsule are known from the prior art. A capsule of this general type is described in British Patent No. 1397116. In this method, water is injected from the top of the cartridge and flows down through the ground coffee, through a filter and finally through a piercing hole or holes of the bottom side. More sophisticated systems are based on a similar approach using trunco-conical cartridges such as in US 2002/0148356 or using rectangular cartridges such as in US 2002/0148357.
One commercially successful capsule system for extracting coffee beverage from capsules consists in placing an air- and water-impermeable capsule into an extraction device, injecting hot water into the capsule until the internal pressure in the capsule reaches the value at which a closing membrane is torn or pierced so that liquid extract can be released out of the capsule. A capsule adapted for such a process of extraction is described in EP 0 512 468. The process itself is described in EP 0 512 470. This method provides a high quality espresso-type coffee. The ground coffee is filled in the capsule fresh and can be stored many months without significant loss of aroma. The release of the coffee is slightly delayed due to a retarded opening of the membrane under pressure from the time water starts to be injected in the capsule. As a result, coffee can be fully extracted under optimal pressure and heat conditions. A stable and thick crema or foam is also produced due to high stress, pressure release and gas-entrapment conditions which are specific to this method.
However, such capsule and process are not optimal for carrying out the infusion or brewing of beverages such as tea or herbal tea.
Therefore, capsules containing leaf tea products and the like have been introduced to the market. It should be understood that the quality of a tea beverage to be prepared is highly dependent on the quality of the leaf tea ingredients, i.e., the tea origin used (soil, drying, blending, etc.) and their storage conditions. For instance, tea ingredients are usually sensitive to oxygen and light. Preferred tea ingredients are taken from loose leaves, chiseled or broken in small fragments. However, brewing conditions are also important to take full advantage of the quality of the ingredients used.
Another problem with tea beverages resides in that taste cross-contamination must be preferably avoided. Taste cross-contamination happens when two capsules are sequentially brewed in the machine and when a taste residue is left by the first capsule on permanent parts of the machine that can consequently affect the taste of the second capsule which is brewed just after the first capsule. For tea, this can be an issue with certain tea varieties that deliver a high aroma profile such as mint tea or other highly flavoured varieties.
WO 2007/042414 A1 relates to a beverage preparation device and a dedicated capsule designed for delivering a brewed liquid at relatively low pressure and is more particularly suited for tea beverages. Thereby, the capsule comprises an enclosure containing one or more beverage ingredients, a filtering wall delimiting at least one filtering side of the enclosure, and an overflow wall that is positioned in the path of the brewed liquid after the filtering wall and which comprises at least one overflow aperture or is associated with at least one puncture means or, respectively, puncture indication means capable of producing or, respectively, indicating at least one overflow aperture.